Brian Armstrong, in Los Angeles, in 2024. Photo: Jason Armond/Los Angeles Times/Getty ImagesThe nation's largest crypto exchange, Coinbase, endorsed the idea of a U.S. bitcoin strategic reserve Friday, part of a wide-ranging blog post on "economic freedom" from CEO Brian Armstrong, shared in advance exclusively with Axios.Why it matters: Armstrong has emerged as the unofficial spokesperson for the industry in Washington, taking a confrontational approach with its chief regulator that others hav...